AT&TFollowsVerizon,MakesDisappointingChangesToItsUpgradePolicy

From June 9, 2013, AT&T customers with contracts ending on March 1, 2014 or later must wait a full two years before having the option of upgrading their handset, rather than the previous period of 20 months, according to the carrier. Naturally, the change will also apply to all of AT&T's new subscribers.
In this respect, AT&T appears to be following Verizon, who earlier this year announced a similar change to its upgrade policy. As explained at AT&T's blog:

Today, we’re announcing a 24-month upgrade policy across all of AT&T’s wireless products and services. This aligns device upgrade eligibility with our standard two-year wireless agreement and it applies to any customer whose agreement expires in March 2014 or later.